US 2002/0060526 A1 discloses a light tube and a power supply circuit. This power supply circuit comprises a serial connection of conventional fluorescent ballast, a rectifier/filter, a pulse-width-modulation switch and a current limiter to be coupled to a light emitting diode array.
Usually, power is delivered from a ballast circuit to a load by providing a certain voltage signal or current signal while the load represents a certain load impedance. The waveform of the voltage signal as supplied to the load is, to a large extent, determined by a waveform of the voltage signal actively outputted by the ballast circuit.